perf(composer-repository): avoid redundant clones when loading async package metadata

load_async_packages cloned each response's version metadata up to
three times (spec_list/response, response_arr, versions_mixed, then
every per-version field) before building the versions Vec. Move
ownership through pattern matches and IndexMap::shift_remove instead.

Measured with laravel/laravel create-project: per-batch response
processing time in load_async_packages drops ~39% (1.30s -> 0.80s
cumulative), narrowing the E2E gap vs upstream Composer from 1.37s to
1.14s on average.

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